Field of Endeavor
The present invention relates to fracturing a geological formation and more particularly to fracturing a geological formation using encapsulated microenergetic material.
State of Technology
Fracking is a technique in which typically water is mixed with sand and chemicals, and the mixture is injected at high pressure into a wellbore to create fractures, which form conduits along which fluids such as gas, petroleum, and groundwater may migrate to the well. The technique is very common in wells for shale gas, tight gas, tight oil, and coal seam gas. Fracturing in rocks at depth tends to be suppressed by the confining pressure, due to the load caused by the overlying rock strata. This is particularly so in the case of “tensile” fractures, which require the walls of the fracture to move apart, working against this confining pressure. Hydraulic fracturing occurs when the effective stress is reduced sufficiently by an increase in the pressure of fluids within the rock, such that the minimum principal stress becomes tensile and exceeds the tensile stress of the material. Fractures formed in this way will in the main be oriented in the plane perpendicular to the minimum principal stress and for this reason induced hydraulic fractures in well bores are sometimes used to determine the orientation of stresses.
It is currently difficult to detect the location, shape, and extent of an underground fracture, such as those created during natural gas extraction by hydrofracturing. It is of considerable interest to know the exact shape and orientation of the fractures and fracture network for design purposes, and to ensure that the rock volume is adequately accessed by the created fractures. Today there is no direct means to do this other than to excavate the fracture, which cannot be done except in extraordinary circumstances. Geophysical methods are used to attempt to image the contrasting properties between the fluid-filled fracture and the rock, but these methods are typically low resolution (meters) by comparison to the aspect of the fracture (millimeters) making it nearly impossible to image the fracture. An additional need is to know the emplacement depth and distribution pattern of proppant. Methods of determining this are currently lacking. The invention describes a method of locating the emplaced proppant material through acoustic emissions of emplaced encapsulated energetic microcapsules.